1. Field of the Invention
Annexes A to F are attached to this specification and the whole content of each Annex is incorporated into this specification.
The present invention relates to a system for generating solid signals and key signals. A solid signal is an electrical signal representing a three dimensional surface of a desired shape. A solid signal is also referred to herein as a xe2x80x98solidxe2x80x99. It may comprise at least one ramp signal and typically comprises a combination of at least two ramp signals which themselves may be modified. It may comprise a signal defined by a polar coordinate system representing a body of revolution such as a circular cone.
2. Description of the Prior Art
Reference will now be made to FIGS. 1 to 3 of the accompanying drawings which show background to the present invention.
FIG. 1 illustrates a known simple wipe between two video sources X and Y.
As the wipe proceeds as indicated by arrow W, video X is replaced across the display by video Y (or vice versa). The effect of a wipe is achieved by mixing the video sources X and Y according to
KX+(1xe2x88x92K)Y
where K is a keying signal. The keying signal K is derived from a xe2x80x98solidxe2x80x99. This will be explained with reference to FIGS. 2 and 3 i.e. a function having a value depending on the h and v co-ordinates within the picture, where v represents line number and h represents pixel position along a line.
FIG. 2 a illustrates a known example of a xe2x80x98solidxe2x80x99 which is a simple ramp. As shown in FIG. 2, a clip level CP is defined. It will be appreciated that over a field or frame, the clip level defines a plane referred to herein as the clip plane. The keying signal K is, in known manner, derived from the solid by applying high gain to the solid and limiting the result, as shown in FIG. 2B. The keying signal has two levels 0 and 1. The transition between the levels occurs where the solid intersects the clip plane CP. The position of intersection is varied, to produce the wipe, by adding an offset to the solid.
FIG. 3 is a schematic block diagram of a wipe generator of a vision mixer comprising a solid generator, a clip element, a gain element, a limiter and a mixer which mixes video sources X and Y in dependence upon the keying signal K.
The solid generator produces a solid, for example a ramp as shown in FIG. 2A. The clip element applies an offset to the ramp to vary the intersection of the ramp with the clip plane CP as shown in FIGS. 2A to 2C. Gain is applied to the offset ramp, in the gain element and the result limited in the limiter to produce the signal K. The amount of gain applied may be varied as shown in FIG. 2B: that varies the slope of the transition between the limit values of the keying signal K.
The mixer mixes the video sources X and Y according to
KX+(1xe2x88x92K)Y.
If K=1, the output is X, if K=0 the output is Y.
If the gain applied to the solid is unity and the clip offset is zero, the solid and the keying signal are identical.
It is desired to provide a system which allows the production of a large variety of wipe patterns. It is also desired to allow the production of new wipe patterns.
According to the present invention, there is provided a system for generating solids and key signals comprising:
n solid generators, where n is equal to or greater than 2;
m key signal generator, where m is equal to or greater than 2;
a cross-point switch having first inputs connected to respective ones of the solid generators, to receive solids,
second inputs connected to respective ones of the key generators to receive key signals,
first outputs connected to respective ones of the key generators for supplying solids to the key generators,
at least one second output; and
control means for controlling the cross-point switch;
the control means and cross-point switch being arranged to:
connect any of the first inputs to any of the first and second outputs; and
connect any of the second inputs to the, or any, second output.
The combination of a cross-point switch with plural solid generators and plural key generators provides a flexible system which allows a large variety of solids and key signals to be produced.
The solid generators connected to the first inputs preferably include any two or more of: plural ramp generators; a polar converter which converts linear ramp signals to polar form for the generation of curved surfaces; a karaoke generator (which is inventive per se) and which generates a solid allowing the production of wipe patterns in the form of bands which progress across a frame; a random generator for generating solids of random dimensions. Other solid generators may be provided. In addition at least one first input is provided for connection to a solid generator external to the system.
An embodiment of the cross point switch has third at least one third inputs and at least a pair of third outputs. Mixing means are coupled to the third outputs to receive solids therefrom and to mix the solids. The mixed solids are coupled to the third input. A mixing means may be coupled to a first pair of third outputs for mixing solids.
A mixing means maybe coupled to a pair of key generators for mixing keys.
A mixing means may be coupled to the output of another mixing means for mixing the output thereof with another solid, for example a solid in the form of random noise.
A recursive mixer may be provided for recursively mixing solids or keys.
Signal processing circuits such as key generators, and mixing means and the recursive mixer, may be arranged to selectively mix and to pass signals unmixed in the case of mixers or to selectively convert solids to keys and to pass solids unconverted in the case of key generators. This allows such circuits to be connected in series to outputs of the cross point switch reducing the number of outputs needed. This also provides flexibility in the processing of keys and solids again increasing the number of solids and wipe patterns which can be produced.
The combination of the cross point switch, the solid generators, the key generators preferably together with mixing means which may be connected in series with key generators and other mixers, provides a potentially very large number of signal paths or routes through the system. Delay means are provided to compensate for the relative delays of different routes. The delay means are controlled by control means which select the routes and thus the delays associated with the routes.
In a preferred embodiment of the invention, the control means provides a fixed set of predetermined routes, and thus a fixed set of delays. Most preferably delays are provided with the routes such that all signals experience the same overall delay from first input to final output regardless of the route taken.